1. Field of the Invention
The present invention relates in general to a bellows for converting pressure changes into linear motion and pertains, more particularly, to a compact metallic bellows for use in restricted space conditions to convert fluid pressure change into precise valve actuator motion. The compact metallic bellows of this invention further provides an illustration of an improved laser welding technique.
2. Discussion of the Related Art
With conventional diaphragms it is generally understood that a single metal diaphragm can be deflected with a fluid pressure to convert the fluid pressure into a precise linear motion. The diaphragm is also compact and will readily conform to available space allowances. The conventional metal diaphragm, however, requires substantial pressures to cause a desired deflection. Another drawback to the conventional diaphragm is its limited maximum stroke and tendency to relatively early fatigue failure.
Conventional metallic bellows have a free length typically much longer than the solid height. These conventional bellows deflect in both axial directions, in compression and in expansion. These bellows take up significant space since their free length is usually substantially greater than their solid height. Furthermore, conventional bellows are not intended to operate at their solid height due to the extreme stress put on the bellows and the bellows joints in the solid height condition.
A substantial drawback of conventional bellows intended for small or compact space applications is that these bellows must operate at or near their solid height. These, operating conditions so shorten the fatigue life of conventional bellows in this highly stressed conditions that standard bellows design and application criteria usually cautions against such use in such severe conditions.
Standard manufacturing methods form bellows in one of three ways. Conventional bellows are made by forming tubing, electrodeposition, or by conventional welding techniques, e.g., gas tungsten arc or plasma arc welding. A new manufacturing technique needed to be developed to make a compact metallic bellows that allows a solid height equal to the free length by providing a welding method that creates a weld no thicker than the thickness of the two adjacent diaphragm members welded together at either the outer diameter edges or the inner diameter edges.
It was believed that a compact bellows would meet the limited space and stroke requirements. This belief has been proven accurate and in the process a unique and novel welding technique has been developed after much trail and error and simply ignoring conventional wisdom in these matters.
Conventional wisdom notwithstanding, a compact bellows has been developed that has a free length equal to its solid height whereby the solid height is accomplished without the stresses normally associated with compressing a conventional bellows to its solid height.
Accordingly, it is an object of the present invention to provide a compact metallic bellows that is adapted to provide a desired expansion by the welding of alternate inner and outer diameters of the diaphragm members. With the compact metallic bellows of this invention the total spring force of individual members is added in series. Thus, while three members are illustrated in the preferred embodiment, the number of members may be selected as a function of the desired working pressure and stroke required.
Another object of the present invention is to provide a compact metallic bellows that is constructed by a laser welding technique that has been discovered to provide an increase in fatigue life and larger stroke available with relatively less pressure available.
A further object of the present invention is to provide a compact metallic bellows in which its solid height and free length are the same or nearly equal, thereby substantially reducing the height and space requirements in which it can be packaged and effectively used.
Still another object of the present invention is to provide a compact metallic bellows that is adapted to lay flat at its solid height. The compact metallic bellows of this invention is low in stress at or near its solid height to optimize fatigue life when operated at or near the solid height.
Still a further object of the present invention is to provide a compact metallic bellows weld fixture that is adapted to laser weld alternating inner and outer diameters of the diaphragm members in the compact bellows assembly. The compact metallic bellows welding fixture of this invention is characterized by allowing the bellows to lay flat but not involving adjacent pieces in the weld.
Another object of the present invention is to provide a compact metallic bellows with a low stress condition at its free length which happens to be its solid height position. Therefore, the basic compact metal bellows construction of this invention is adapted to operate in a region of optimum fatigue life.